在无向图中打印循环

Question

这是我的代码在无向图中进行循环检测

#include<iostream>
#include <list>
#include <vector>
#include <stack>
using namespace std;

class Graph {
    int V, index;
    const int N = 100000;
    list <int> * adj;
    vector<bool> visited;

    // parent stores the parent node of the visited node, this is used 
    // for finding cycle in an undirected graph

    vector<int> parent;

    bool isCycle;    
    
public:
    Graph(int V);

    ~Graph () {
        delete [] adj;
    }
    void addEdge(int src, int dst);
    void set_index();
    void DFS_isCycleUntil(int src);
    bool IsCyclePresent();
    void printCycles(int edges, int mark[], int& cyclenumber);

    
};

Graph::Graph(int V){
           this->V = V;
           adj = new list<int> [V];
           this->index = 0;
           visited.resize(V, false);
           parent.resize(V, -1);
           isCycle = false;
}

void Graph::set_index()
{
    this->index = 0;
}


void Graph::addEdge(int src, int dst) {
    adj[src].push_back(dst); // push back to add to the linked list
    adj[dst].push_back(src);
 }

void Graph::DFS_isCycleUntil(int src) {
    visited[src] = true;
    
    for (auto& adj_V: adj[src]) {
        if (!visited[adj_V]) {
            parent[adj_V]=src;
            DFS_isCycleUntil(adj_V);
        } else if(parent[src] != adj_V) {
            isCycle = true;
            return;
        }
    }
}

bool Graph::IsCyclePresent() {
    return isCycle;
}


int main()
{

    Graph gdfs(6);

    gdfs.addEdge(0, 1);
    gdfs.addEdge(1, 2);
    gdfs.addEdge(2, 3);
    gdfs.addEdge(3, 4);
    gdfs.addEdge(4, 5);
    gdfs.addEdge(5, 2);

    gdfs.DFS_isCycleUntil(0);
    cout << " Depth-first traversal for the given graph: "<<endl;
    cout << "cycle present: " << (gdfs.IsCyclePresent() ? "true" : "false")<< '\n';
    return 0;
}

我想打印出每个检测到的周期。我已经看到了 geekforgeek 的一些尝试，但恐怕我无法遵循它......这可能是错误的。 我想知道任何人都可以提出一种有效的方法来包含一个打印功能来打印出所有检测到的循环的路径？

Answer 1

每当我们在DFS_isCycleUntil 中遇到循环时，我们都可以调用printCycle。

void printCycle(int cur, int par)
{
    if (cur == par)
    {
        cout << cur << endl;
        return;
    }
    cout << cur << "->";
    printCycle(parent[cur], par);
}

void Graph::DFS_isCycleUntil(int src) {
    visited[src] = true;

    for (auto& adj_V : adj[src]) {
        if (!visited[adj_V]) {
            parent[adj_V] = src;
            DFS_isCycleUntil(adj_V);
        }
        else if (parent[src] != adj_V) {
            isCycle = true;
            cout << adj_V << "->";
            printCycle(src, adj_V);
            return;
        }
    }
}